In recent years, a technique for communication using an IP (Internet Protocol) network called VoIP (Voice over IP) was developed as broadbandization of access networks using ADSL (Asymmetric Digital Subscriber Line), FTTH (Fiber To The Home), and the like was dramatically distributed.
As such a network, a network called an NGN (Next Generation Network) capable of performing video image communication, high speed data communication, and the like as well as sound communication was also proposed, for example.
On the other hand, the IETF (Internet Engineer Task Force) which is an organization for internet standardization defines SIP (Session Initiation Protocol). SIP is a protocol which was standardized as a technique for realizing real time communication (for example, an IP telephone, a video meeting, and the like) on an IP network.